Screw-type implants are now well-known. U.S. Pat. No. 3,499,222 of L. I. Linkow et al. discloses screw-type implants which may be buried in the alveolar ridge crest bone of a patient in an edentulous region. The implant has a threaded lower portion which may be screwed into an opening created in the bone after the tissue has been displaced. A coronal portion protrudes above the bone and is used to support an artificial dental appliance, e.g., an artificial tooth or bridge.
In more recent years, submergible implants have been created in which the threaded portions of the implants can be completely embedded in the bone. They may then be covered with tissue and allowed to remain in place while new bone grows around the implant and through vent holes within the implant. Once it is firmly anchored in new bone, the tissue is reopened and an abutment or upper post portion is screwed into the implant portion and is used to mount the artificial dental device. Submergible implants of this type are disclosed in U.S. Pat. No. 4,713,004 of Linkow et al.
It is advantageous, when installing an implant portion in the patient's jawbone, for the implant to self-tap into the bore hole created in the patient's jawbone because this causes the implant to be better anchored in the bone. As shown in U.S. Pat. No. 4,713,004 of Linkow et al, such an implant may include a cylindrical body with an exterior threaded region that contains a longitudinal channel through a portion of the outer parts of the threads. The channel is wider toward its bottom. One side of the channel is at a right angle to the implant circumference so as to create a cutting edge that creates a self-tapping capability for the implant when it is threaded into a bore or opening in the patient's bone. The channel guides bone chips, created during the threading of the implant, toward the base of the bore in the bone. The bone chips created during the self-tapping operation promote faster bone growth due to their autogenous nature.
The majority of submergible dental implants sold today have an external hexagonal head ("hex-head") which projects from the outer end and is used to couple the implant to an insertion device, e.g. a wrench. This projecting hex-head is also used in attaching the implant to an abutment or post having a matching hex-shaped cavity that receives the projection. Such projecting heads and cavities may be referred to as "coupling surfaces."
Certain areas of the jawbone, such as the thin ("bucco-lingual") residual ridges located primarily in the maxilla, are too thin to allow drilling with a cylindrical drill of The preferred size range in order to create the bore hole. This, in turn, leads to the use of narrower implants. However, due to the decreased surface area of bone contact and their small diameter, these narrower implants are much more likely to fail.